Impact point development for golf clubs

ABSTRACT

A golf club with a gripping section at one end and a club head having a heel portion and a toe portion, attached to the shaft at the other end wherein said shaft centerline and a plane parallel to the ground and tangent to said heel form a lie angle when said club head is at rest and positioned to strike said golf ball; a club head whose mass distribution is concentrated at said toe and heel; a club face on said club head operable for striking a golf ball and spanning the area between said heel and said toe of said club head and having a heel to toe and sole to the top of club head bulge defined by a radius whose center is offset toward said heel and whose arc is swept from heel to toe of said club face; a lie angle configured to maintain the impact point of said golf ball on said club face when said impact point is off the center of mass.

BACKGROUND

[0001] 1. Field of the Invention

[0002] The present invention relates to the design of golf clubs and in particular to the design of the driver, fairway woods, and utility woods.

[0003] 2. Description of Related Art

[0004] The new technology advances in head design and especially in shaft design have made possible the fabrication of longer lighter clubs, especially in the woods. This has been used to market clubs that are claimed to hit the ball further and be easier to use because of their longer length and lighter shaft weight. However, in general, the lengthening of the shafts of the club have made it harder to hit the ball consistently in the center of the face, and therefore has decreased the distance achievable with these new clubs, rather than improving these characteristics.

[0005] Data published in the Golfsmith Technical Journal in Feb 1998 on the variation of the impact point of the ball on the club face as a function of shaft length shows a consistent and predictable pattern. It is a pattern that is also observed in the wear patterns on the faces of drivers and irons used by the golfing public. This pattern can be bounded by an ellipse, with the elongated axis being perpendicular to the golfer's swing plane. The major axis of this ellipse is about 2 inches in length, and the minor axis is about 1.1 inches in length. The impact point pattern found for a 45 inch driver at Golfsmith is shown in FIG. 1. With the standard lie angles for the woods, as the club shaft length increases the centerline of the impact ellipse moves off the top of the club face, leading to fat, skyed shots.

[0006] Since the standard lie angle for golf clubs has been established from experience, it is observed in the designs of the major club makers. This angle is the angle subtended by a line drawn down the centerline of the shaft, and a horizontal line which is tangent to the sole of the club at the contact point that rests on the ground at address. The standard lie for a driver is 54 to 55 degrees. However, it has been found by analysis that this lie angle combined with even standard length woods does not fit the general population. For the majority of the population the butt height of the club lies in the range of 30 to 33 inches.

[0007] For shorter players and women it can go as low as 28 or 29 inches. An analyses show that the actual setup angles for driver lengths of 42 to 46 inches range is from 40 to about 50 degrees. This is compared to the lie angles provided by the manufacturers, which range from 54 to 56 degrees. The reason for this difference can be deduced from performance; even with these lie angles the impact point of the ball is still moving off the top of the club face. It would be worse with the lower lie angles, so that 54 to 56 degree lie angle approach was adopted by designers many years ago.

[0008] The following photo demonstrates the optimum setup parameters for the hands and the club position. This is demonstrated by a picture taken in the GE laboratory in 1932, and is still viable today. Jim Reynolds personified the modem ideal setup and hand position to the ball even though this photo was taken 70 years ago. His arms are vertical and his hands are low and set up to the ball with a 45 degree shaft angle, shown by the white lines.

[0009] His right hand is aligned along the shaft so that he transfers power to the ball along the line to the target, and his left hand is firm and angled up so that he overcomes the effects of gravity, and keeps the club aligned on the ball.

[0010] The swing plane defined by the dotted line from the ball to his shoulder is 60 plus degrees, which is consistent with the face impact data that has been gathered from other sources.

[0011] This shows the typical setup parameters of 45 degrees for the driver setup angle, and 60 plus degrees for the swing plane angle.

[0012] The swing plane angle of 60 plus degrees influences the diagonal angle that defines the major axis of the miss ellipse shown in FIG. 1. The explanation of the motion of this miss area is shown below. Descriptions of the behavior of the club during the downswing of a number of professional golfers have been examined, and the following conclusions have been reached:

[0013] As the club head is accelerated through the ball, there is a very large increase in the head speed in a very small time increment, as the hands release into the ball. This action and the forces associated with it has been the focus of many training and swing analyses. However, there is another force which tends to be overlooked, and that is the force of gravity on the club head, which operates continuously on the head, pulling it down towards the ground.

[0014] Analysis of Charles Howell, an excellent young pro, shows the relative timing of the segments of his downswing. These can be correlated with the shaft deflection curves for other pros to derive the predictions of the forces on the hands of the golfer during the golf swing. At the time of the release of the hands through the ball, Howell is ⅔ rds of the way down from the start of the downswing to impact.

[0015] The majority of the acceleration through the downswing occurs during the last third of his downswing, where the club approaches the horizontal position that it has at impact. The time for this increment of the downswing is about 0.15 seconds for professional golfers. During this period, there is a torque on the hands of about 15 ft-lbs. associated with the horizontal acceleration of the club head into the ball, and a lesser, but significant torque in the vertical plane due to the inexorable pull of gravity on the club head equal to about 1 ft-lb.

[0016] If this is uncompensated the club head would drop about 7 or 8 inches during this short time. Even if the gravity pull is 90% compensated by the golfer, the club head would drop about 0.78 inches, and this motion is normal to the swing plane. So the impact point of the ball moves diagonally up and towards the toe about 0.8 inches if the gravity force is not compensated. It is noted that the increase in torque (closely correlated with swing weight) on the golfer's hands is about 7% for an increase of 3 inches in the shaft length of the driver from the standard of 43 inches to 46 inches. If this is uncompensated by the golfer, as discussed above, this will result in the motion of the impact point on the face up and towards the toe by about 0.7 to 0.8 inches. The effect of the gravitational pull on the head is shown in the following diagram:

FIG. 3. SHOWS THE FORCES ON THE CLUB HEAD LINKED TO THE SWING PLANE ANGLE

[0017] The gravity force component, if uncompensated will cause the head to move downward and inward towards the golfer, which causes the ball impact point to move from the center of the face to a point diagonally upward towards the toe of the club. The other gravity component, which is parallel to the swing plane, exerts a pull on the hands which is compensated by a firm grip on the club.

Discussion of the face dimension design for the new club concept

[0018] The diagram below shows the relationship of the club design parameters to the location of the miss ellipse on the face of the club. The miss ellipse, from the above test data, is approximated by an ellipse with a major axis dimension of 2 inches, and a minor axis dimension of about 1.1 inches. The ball impact circle diameter, caused by the compression of the ball at impact, has been estimated from 0.7 inch to as much as 0.92 inches for the stronger hitters now on tour.

[0019] Using the larger ball impact diameter figure, it can be seen that the miss ellipse impact area is formed by the overlay of multiple ball impact areas, showing that the locus of the center of these ball impact areas is close to a line perpendicular to the swing plane angle. For the larger ball impact circle diameter of 0.92 inches, the length of this perpendicular line is 1.08 inches, i.e.; 2-.0.92 inches.

[0020]FIG. 4. The miss ellipse is linked to the swing plane angle, and its long axis is perpendicular to this plane as seen in the test data. Thus for an average golfer, if a mean swing plane angle is 60 degrees, and his setup shaft angle is 45 degrees, with a standard 55 degree lie angle, the impact ellipse is tilted up at 20 degrees to the horizontal axis of the face Using trigonometry, it can be seen that the height of the impact ellipse at the toe would be 0.83 inches, or 21 mm above the center of the face. On a standard driver face, this would put the top of the miss ellipse near or off the top of the face.

[0021] Alternatively, if a new driver design configuration is used, with a lie angle of 61 or 62 degrees, and a face tilt up towards the toe of 5 degrees, with the same swing plane angle and shaft setup angle, the centerline of the face will be aligned within 9 degrees of the miss ellipse centerline. This will lower the top edge of the miss ellipse by 10 mm, and bring the expected impact points for the ball much closer to the sweet spot in this new design.

[0022] The face height of a stainless steel driver is limited to about 44 mm, or 1.732 inches, because of the limited volume of the head designs. The new design concept will keep the generic miss ellipse ball impacts well within the optimum hitting area, even on the face of a generic stainless steel driver. Analysis of a titanium head yields even better results. For a typical face height of 50 mm for a titanium head design, the center to face top height would be 0.984 inches, which would provide even a greater margin to keep all ball impact circles on the face of the club. This new design with a more upright lie and up-tilted face, will optimize the performance of the club for center hits and for the most common mis-hits towards the toe of the club.

[0023] A diagram showing these concepts is shown in FIG. 4.

[0024] An Autocad drawing is shown of a prototype driver head that was fabricated in 1999, which embodied the new design concepts described above.

[0025] FIG 5. The autocad drawing is shown above. The new driver was fabricated in Dec 1999, and was successfully tested in Jan 2000 and April 2000. These tests were performed at the Impact Golf Technologies facility in Ft Worth, Tex., using Iron Byron and the instrumented test range at this facility. The test results were very impressive, and showed that the center hits produced longer drives than the control club, and was very superior in performance for toe hits. Detailed plots of these results are shown in the plots.

[0026] These tests were performed in April 2000 with Iron Byron with a 95 mph head speed, and using a set of Strata balls. The center hits were in the sweet spot of the face, the toe hits were offset 0.5 in towards the toe, and 0.5 up from the centerline of the face, and the heel shots 0.5 in towards the heel from the sweet spot. Thus the toe hits were almost ¾ inch offset, and the result was only a 2 yard difference in range, and a 5 yard left offset. This performance is considered to be excellent, and much better than would result from a club with a standard lie. The heel performance yielded a 10 yard range delta, and a 5 yard left offset, also considered to be good performance.

[0027]FIG. 6. Tests with amateur golfers have also produced excellent results, in terms of accuracy and distance compared to the clubs they had been using. Result have been good for golfers with handicaps from 8 to 25, and have been consistent and repeatable. The 8 handicapper consistently hits this driver over 300 yards, with most of his hits in the fairway. Although he is a naturally long hitter, none of the drivers he was using previously compare with the results produced by this driver design, either in distance or in accuracy. 

What is claimed is:
 1. A golf club with a gripping section at one end and a club head having a heel portion and a toe portion, attached to the shaft at the other end wherein said shaft centerline and a plane parallel to the ground and tangent to said heel form a lie angle when said club head is at rest and positioned to strike said golf ball; a club head whose mass distribution is concentrated at said toe and heel; a club face on said club head operable for striking a golf ball and spanning the area between said heel and said toe of said club head and having a heel to toe and sole to the top of club head bulge defined by a radius whose center is offset toward said heel and whose arc is swept from heel to toe of said club face; a lie angle configured to maintain the impact point of said golf ball on said club face when said impact point is off the center of mass.
 2. A golf club as claimed in claim 1 wherein the lie angle which is the angle between the centerline of the shaft and a horizontal plane tangent to the sole of the club is greater than about 60°.
 3. A golf club as claimed in claim 2 wherein the length of the shaft measured from the connecting point to the head and the butt end is between about 39′ and 48′.
 4. A golf club as claimed in claim 2 wherein height of the face of the club measured from the tope edge to the sole edge at its greatest point is about 1.732 inches.
 5. A golf club as claimed in claim 1 wherein the distance from the center of the face to the top edge is a about 0.984 inches for titanium.
 6. A golf club as claimed in claim 1 wherein the face is tilted upwardly at an angle of about 5°.
 7. A golf club as claimed in claim 1 wherein an angle made by club face to the horizontal plane tangent to the sole of the head is about 5°.
 8. A golf club as claimed in claim 1 wherein the mass of the club head is concentrated in predetermined area and combined with said preferred lie angle provides an elliptical zone on the face of the club whose major axis is generally perpendicular to the shaft and wherein hits in the zone produce generally the same distance as hits at the center of impact.
 9. A golf club as claimed in claim 1 wherein the mass concentration is higher in the toe and lower in the heel to maximize the moment of inertia about the axis extending perpendicular to the diagonal passing through the center of the face. 